How Living Things are Alike

Living things may be different in many ways, but they are alike in important ways:
1. Every living thing on the earth came from another living thing. A snail's parents are snails, and its young will be snails. They will grow and produce more snails. A watermelon plant grew from the seed of another watermelon, and its seeds can grow up to produce watermelon plants. These plants will produce more watermelon plants. Living things reproduce living things of the same kind.
2. Living things are made of cells of protoplasm. Whales and oak trees, mice and grass -- all are made of cells. A cell is a tiny package of living substances which together are called protoplasm. Some of the protoplasm is in liquid form, more or less like the white of an egg. Protoplasm consists mainly of different kinds of proteins. Some of the protoplasm is the container part of the package. It is called the cell membrane. Most cells have a part made of thick protoplasm, called the nucleus.
3. Living things grow and change. Living things grow by increasing the number of cells or the amount of protoplasm.
4. All living things need food. Living things use food as material for growth and as fuel for energy.
5. All living things need oxygen. The oxygen is used by the cell in getting energy from food.
6. Living things can move. The energy for movement comes from within the living thing. It comes from food.
Nonliving things can move, too. A tin can may roll down a hill or be blown by the wind. But the energy for this movement comes from outside.

Animals and Plants

After a scientist decides that a thing is living, he classifies it as an animal or a plant. Plants resemble animals in many ways, but they are different in these important ways:
1. Most plant cells have a thick, nonliving wall around the cell membrane.
2. Green plants can make food out of substances that are not food. In photosynthesis green plants take in carbon dioxide and water to make food.
3. Most plants do not move very much or very fast, compared to animals. Plants move when they grow. Stems grow and move up; roots grow and move down. Petals move when flowers open and close.

In Between Animal and Plant

We have just divided the living things of the world into two main groups -- plants and animals. But here again, everything does not fit. There are tiny living things that can be classified as either plants or animals, or neither. They are called euglena. After you find out more about classifying plants and animals you might try to decide where you think they belong, and why. Then look it up in an encyclopedia and find out what scientists say.